1. Field of the Invention
The present invention relates generally to a mechanism for diverting signatures in a web fed rotary printing press, for example within a folder unit of the printing press.
2. State of the Art
Commercially available web fed rotary printing presses typically include printing units arranged at fixed locations in the press room. After the web has moved through the printing units, it is transported to folder and cutter units that fold the web and cut the web lengthwise and crosswise into printed products, such as signatures used to create newspapers, magazines, and the like. The web is cut into signatures that are typically conveyed to a fan or other delivery system, which deposits them on, for example, a conveyor belt. The printing press can be configured so that signatures are evenly diverted among several fans or other delivery systems using a diverter mechanism. Known diverters can undesirably mark the web and signatures cut therefrom. Known diverters also lack positive control over the web and signature transport path, which can lead to additional web and signature damage, and to jamming of the press.
One known diverter illustrated in FIGS. 1A and 1B includes a wedge 108 that is rotatable to divert signatures to one side of the web or to the other side of the wedge. The wedge is placed in a signature stream path 101 with an apex of the wedge facing the oncoming stream. There is a gap between consecutive signatures traveling along the paper stream path. At each gap, the wedge 108 can be rotated so that the wedge 108 will deflect the next signature to the other side of the apex. Such a configuration typically includes a nip 102 located upstream of a cutter 104 having first and second cutting cylinders 105 and 107, and a nip 106 located downstream of the cutter 104. Signatures exiting the nip 106 are deflected by the wedge 108 to either of the fans 110, 112 shown in FIG. 1A, or to either of the conveyor paths 114, 116 shown in FIG. 1B.
Such a diverter mechanism has several disadvantages. For example, the movable wedge can cause marking of images printed on the signatures and an increased risk of having signatures jam in the printing press. The wedge also lengthens a distance the signatures travel without being under positive control, because the signatures are not under positive control as they travel along the sides of the wedge. A lack of positive control increases a likelihood that the web and signatures will not travel precisely and smoothly through the printing press, and increases potential jamming, potential misalignments, and potential wrinkling, tearing, and signature damage.
Other diverters suffer similar drawbacks. For example, U.S. Pat. No. 4,373,713 to Loebach discloses a sheet diverter located in a stream of signatures and having a pair of movable diverting cylinders provided adjacent to the signature stream. U.S. Pat. No. 4,729,282 to Kasdorf describes a diverter including a stationary wedge located with an apex pointed into a signature flow direction, and two diverter rolls forming a nip, each of the diverter rolls having an eccentric rotational axis. However, the diverters described in these patents have several disadvantages.
For example, U.S. Pat. No. 4,373,713 to Loebach requires a matching of the speeds of two diverter cylinder surfaces with the speeds of the signatures to minimize marking and to maintain a smooth flow through the diverter. Different diverting cylinders are required for each signature size, and the distance which the diverting cylinders will deflect the paper stream depends on camming surface contours included on the diverter cylinder surfaces and on radii of the diverting cylinders, which are typically not adjustable. Because the camming surfaces do not firmly grasp signatures passing between the diverting cylinders, the signatures are not under positive control as they pass between the diverting cylinders over a distance equal to at least an average diameter of one of the diverting cylinders.
U.S. Pat. No. 4,729,282 to Kasdorf requires that rotation of two diverter rolls be carefully synchronized. In addition, the wedge used lengthens a distance the signatures must travel without being under positive control, and the wedge can cause marking.
U.S. Pat. No. 5,538,242 to Doucet discloses a signature aiming device having two cylinders that are offset along an axis of a signature flow path. The device is provided with tapes or belts that flow along substantially the same path to the cylinders, and then partially wrap around each cylinder and flow away from the cylinders in different directions. Signatures flowing along the path toward the two cylinders are sandwiched between the tapes until they are released when the tapes diverge as they wrap around the cylinders.
However, the device disclosed in the Doucet patent does not maintain positive control over signatures throughout the transport path. The signatures are transported by pressing the signatures between two tapes, and tapes provide less positive control than nips that firmly grip the signatures. The tapes also increase overall complexity of the device, and any difference in speed between the two tapes can damage the signatures and increase the likelihood of jamming within the printing press. Furthermore, staggering the two cylinders as disclosed in the Doucet patent requires a distance between the two cylinders along the signature flow path, where the signatures are unsupported on one side. At a minimum, the signatures are not positively controlled over the sum of the distance between the two cylinders along the signature flow path, and the distance between the last cylinder and a receiving mechanism, such as a fan or another tape transport system. The absence of positive control over the transport path can lead to damage of the web and signatures, and to jamming of the press.
U.S. Pat. No. 5,702,100 to Novick et al. discloses a diverter for signatures in a folder apparatus within a printing press. A set of high-speed tapes convey signatures to a diverter, which selectively redirects the signatures. The diverter of the Novick patent includes two rotating assemblies which each include at least two rollers. When the assemblies are rotated in coordinated fashion, the outer edges of the rotating assemblies describe overlapping arcs.
The diverters illustrated in the Novick patent have several disadvantages. For example, rotation of both assemblies must be carefully coordinated to alter the exit angle from the nip. This coordinated rotation requires a relatively complex actuator/control mechanism that is powerful enough to rotate the assemblies with a speed sufficient keep up with the flow of signatures between the assemblies. In addition, the diverters shown in the Novick patent use tapes which result in a loss of positive control over the web and signatures, and that can lead to damage of the signatures and jamming of the presses.
European Patent Application No. EP 0 297 282 B1 discloses cutting cylinders that are moved together as a unit laterally with respect to a web path that flows between the cutting cylinders. For example, FIGS. 1 and 2 of the European Patent Application show cut signatures flowing out from between cutting cylinders 7 and 8 on one side or the other of a wedge 15, and being guided to one of two receiving paths formed by tapes 16, 17 and 21. However, the use of the wedge 15 and associated tapes has various disadvantages such as marking of the signatures and a loss of positive control.
Accordingly, it would be desirable to provide a diverter that will accommodate high press speeds, without marking or otherwise damaging the web and signatures. It would also be desirable to provide a diverter that can permit positive control over the web and signatures to be maximized so that the potential for damage to the web and signatures, and the potential for press jamming, can be minimized.